In this photo dated Feb. 1, 2013, Malian soldiers patrol the streets of Timbuktu. Heavy gunfire erupted on March 31, 2013 in Timbuktu as Malian troops were combing the city for infiltrated jihadists following a suicide attack.

The assault launched late March 31 by jihadi fighters on the northern Mali town of Timbuktu reflects the changing security scenario in West Africa. On the one hand, the Franco-African military intervention against groups allied with al-Qaeda in Islamic Maghreb (AQIM) has inflicted considerable losses on Islamist militias — including within their leadership — and forced extremists who previously occupied the northern half of Mali to retreat to the mountainous border with Algeria to escape further fatalities from ground and air assaults. That progress allowed French President François Hollande on March 28 to outline his planned withdrawal schedule for France’s forces.

But Sunday’s infiltration and attack on Timbuktu by a small unit of radicals not only demonstrates that the otherwise battered extremists are determined to continue waging jihad despite the setbacks they’ve suffered. It also suggests Islamist militias are already reverting to traditional methods of using the vast, ungovernable Sahel region to avoid enemy forces as they orchestrate regular strikes against military, government and civilian targets in Mali, Mauritania, Algeria and Niger.

“The military intervention has decimated Islamist forces and killed key leaders, but no one ever believed it would eradicate jihadi groups in the Sahel,” says a senior French counterterrorism official who cannot be quoted by name. “Surviving commanders and fighters are now regrouping and gradually resuming operation, and will seek to regain some of the influence they had before they made the mistake of taking over the entire northern half of Mali. They’re reverting back from being a terrifying occupation force to being a more elusive force of terrorism.”

As that happens, the official says, Islamist groups are expected to increase kidnapping, attacks on military outposts and, throughout the Sahel, suicide strikes on targets that they staged before teaming up with Tuareg militants to seize control of northern Mali in April 2012. Though that activity — which never entirely ceased during their domination of northern Mali — will remain a threat, it’s a far cry from the acute security risk that surging jihadi forces had posed to international security and West African stability while ruling such a vast area. With that menace significantly beaten back, Hollande announced on Wednesday night that he’ll withdraw half of France’s 4,000 troops by July and bring another 1,000 home by year’s end.

But French security officials say that an even earlier Hollande announcement was just as important in reflecting the evolving security situation in West Africa. On March 23, Hollande confirmed reports that Chadian soldiers had killed Abdelhamid Abou Zeid, AQIM’s regional Sahel commander. An Afghan-trained fighter responsible for the kidnapping of Western hostages — two of whom he is thought to have personally executed — Abou Zeid was replaced March 24 by fellow Algerian Djamel Okacha, 34.

Like Abou Zeid, Okacha is a trusted lieutenant of AQIM’s top leader and fellow Algerian Abdelmalek Droukdel. Okacha’s participation in much of the most successful and deadly Sahel terrorist activity of the past decade is believed to have been as crucial to him being tapped to succeed Abou Zeid as his fidelity to Droukdel.

“There aren’t lots of actors in Sahel or North African jihadi groups who have the background and character allowing them to assume command of entire networks,” say a French intelligence official. “Not many have the experience, trust, and cruelty required.”

There may be even fewer than suspected. French officials continue trying to verify claims that Chadian troops also killed notorious militia commander Mokhtar Belmokhtar (an excellent bio of whom can be read here). An Afghan veteran who split with AQIM to found his own independent but allied network, Belmokhtar has operated his smuggling, trafficking, kidnapping, and commando activity in the Sahel area since the mid-1990s. During that time, Belmokhtar fully integrated his operations into local populations, sharing his criminal proceeds.

That influence earned Belmokhtar acceptance among nonradical Sahel residents — and the reputation as an effective, savvy leader among his devoted fighters. Some of those were among the more than 30 militants who stormed Algeria’s In Amenas gas plant in January in purported revenge for the French intervention in Mali. During the ensuing siege Belmokhtar’s fighters killed 37 foreign workers, before being slain themselves in a military offensive.

If — like Abou Zeid’s death — Belmokhtar’s demise can be confirmed, it won’t prevent the region’s jihadis from continuing to plot and attack, French authorities say — but it could seriously undermine their ambition and effectiveness.

“There just are many men with the influence and authority that can order that many fighters to mount a strike they know they’ll die in without any questions being asked or challenges made,” says the French counterterrorism official, referring to the gruesomely spectacular In Amenas attack. “If Belmokhtar’s death is confirmed, it won’t be decisive to the existence and operation of his group, but it will have serious consequences. The same is true of Abou Zeid. Any significant disruption of extremist activity is good for us, because disruption always bad for them. You could say disruption was what the Mali intervention was mostly about.”